Various systems rely on evaporating water to provide cooling. For example, evaporative coolers, commonly referred to as swamp coolers, have been used for years to cool houses. These coolers drive air through a water soaked pad and the air is cooled as the water evaporates.
Fans have been fitted with nozzles to spray a mist of water into the air stream produced by the fan, and are commonly referred to as mister cooling systems. Such systems are often seen at sporting events. The moving air is cooled by evaporation of the mist carried in the air stream. For mister systems to be efficient, it is necessary to atomize the water, i.e. reduce the water to minute particles or droplets, producing the largest surface area possible and the quickest evaporation rate. This has required large, high pressure pumps to provide a flow of water at greater than eight hundred pounds per square inch, psi, to mister nozzles. Powerful motors have been used to drive the pumps. The systems are relatively heavy and expensive.